Traditional methods of enhanced oil recovery include gas, thermal, and chemical injection techniques. Gas injection, commonly utilizing injection of carbon dioxide (CO2) through a series of boreholes, allows for oil recovery from adjacent recovery wells. In its traditional form, EOR is based on the use of recognized basic tenants of physics: first, oil formations are composed of multiple, irregular lenses retaining oil which combine to form formations and reservoirs; second, depending on viscosity, all fluids seek the path of least resistance when traveling through an oil formation; and third, water is not miscible with oil and has a higher viscosity than a gas like CO2; fourth, CO2 is miscible with oil and will interact with and energize oil in formation; and fifth, CO2 has the ability to travel through numerous lenses within a formation that water will not initially enter.
Conventional and traditional methods of EOR will “water flood” first by entering all oil lenses that will accept water. As a result, lenses into which water can enter will have the oil partially pushed out of the lens and replaced with water. CO2 is then injected into the reservoir. It will bypass the water filled lenses and seek another lens with less resistance. The CO2 will energize the oil in the new lens and promote movement of the oil out of the lens. Subsequently, water will be injected behind the CO2 to push everything out of the lens, leaving the lens filled with water. This procedure will be repeated to maximize the recovery of oil from the reservoir until such time as the results no longer yield economic favor.